I. Field of the Invention
The invention relates to a pavement marker having a retro-reflector and a method of manufacturing the pavement marker and, more particularly, to a low profile pavement marker adapted to be mounted on the roadway surface to reflect light from headlights of an oncoming automobile to delineate traffic lanes of the road.
II. Description of the Prior Art
Reflective roadway markers are used by highway departments and others for delineating highway lanes. Properly designed reflective markers are clearly visible at night by reflecting light from an oncoming vehicle back to the vehicle. Such markers generally include a body and at least one reflective lens supported by the body.
Cube corner type plastic lens such as disclosed by Balint, et al, U.S. Pat. No. 3,409,344 are frequently used in pavement markers. Balint discloses a roadway marker including a housing molded in situ about a plurality of reflective inserts, the inserts having a substantially flat outer surface and a plurality of retro-reflective prisms on their inner surfaces. The inner surface of the prisms are coated with a metalized layer. The entire housing is filled with plastic material in order to provide strength and rigidity to the marker.
It is also known to incline the flat surface of the lens at a predetermined angle with respect to the roadway surface so that the self-cleaning of the lens is provided by the passing of a tire over the lens. The angle that the reflective lens makes in relation to the pavement surface effects the relative efficiency of both the cleaning and the efficiency of the retro-reflective prism surfaces. It is generally desired to select an angle so that the reflective efficiency of the prism surface is maximized. However, cube corner lenses are typically made of an acrylic plastic which is brittle and frequently is cracked or broken. Likewise, these markers are frequently dislodged from the roadway surface.
Because the handling of an automobile is effected by the passing of its tire over the pavement marker, it is desirable to have as low a profile marker as possible to avoid distorting the handling characteristics of the automobile. However, since the lens of the pavement marker must reflect a predetermined amount of light, such as three candle power, as required by the highway departments, it is necessary to produce a lens with sufficient reflectors to reflect this amount of light.
Thus, it is desirable to provide a reflector which has a low profile and sufficient retro-reflectivity. Likewise, it is an object of this invention to provide a pavement marker which is strong and adheres well to the road.